All morality that was ever developed in any tradition in the world can be reduced to the principle of acting as one acts toward those with whom one belongs. And the differences between the different codes of morality are only the limits that we draw for belonging: “These are the ones toward whom you have to act morally, and the others are ‘the others,’ outside.” And when you really live with common sense, that has no limitations; you live out of a morality that includes everybody, and therefore you behave toward everybody as one behaves when one belongs. That is what Jesus meant when he said “the kingdom of God”—and any other term of that sort that you get from any religious tradition will fit in here.
—from the book The Way of Silence: Engaging the Sacred in Daily Life
by Brother David Steindl-Rast